The incredible precision of LEGO parts makes them attractive for building precise jigs, but the fact that they can come apart fairly easily isn't so helpful for this application. Can anyone recommend methods and materials for gluing LEGO bricks together to create permanent assemblies?

I'd prefer to avoid thick adhesives like epoxy or hot melt glue, as I suspect that those might make it difficult to get the bricks to snap together completely. I think most bricks are made of ABS plastic, so I'd guess that a solvent like acetone might work to weld them together, but I've never tried it. Does anyone have experience gluing bricks together?

@Kramii I hear you! When LEGO bricks are used as a toy, the ability to take them apart and turn them into something else is an essential part of the experience. When used as a tool, however, the fact that they can come apart pretty easily can be a liability. It's not easy to think about bricks as consumable instead of reusable, but when you do there's a whole other world of things you can do with them!
–
CalebJan 26 '12 at 6:38

I'm actually interested in this question for repairing some old broken bricks and base plates.
–
JeremyFeb 3 at 15:04

13 Answers
13

The LEGO Group have recently started using solvents to "weld" elements together (notably the Minifigure legs to the magnet blocks), which are fairly heavily controlled in pure forms in most countries under drug legislation.

I have discovered that LEGO is not using glue at all, but a solvent, that actually loosens the surface of the ABS plastic and allows the molecules to combine. Once the solvent evaporates, it leaves behind a cleanly fused surface with no residue at all.

Reading further on the subject, I found that LEGO has been using two types of solvents. One is called MEK (methyl-ethyl-ketone) and at some point they switched to GBL (gamma-butyrolactone). I’m no chemist, so I had no idea what these are, but I read that both of them are water soluble at certain temperatures. So, I thought to try loosening the seal between the minifig and the magnet by hot water.

However, as the opaque LEGO bricks are made from a styrene based plastic (ABS), most "Plastic Cement" or "Polystyrene Cement" glues should work to fix your parts together permanently (as these typically contain the same solvents as TLG use, i.e. MEK/Butanone). As with most other plastic gluing projects, care should be taken around transparent elements, as well as ensuring you don't use too much and have it leak over the exterior of your model.

You only need acetone, no need for other products or ABS chips.
Just brush acetone on both pieces, join them and wait 5 minutes.
You will find that your two pieces now are literally one piece.
There is not anything stronger for abs plastic.

You can get 100% concetrated acetone at the hardware store, or at beauty supply stores.

If you don't mind a little extra work, using melted ABS is probably your best bet, you just need to chop up some scrap ABS into shavings (I used a big drill bit on some ABS and it made shavings very quickly), and then put them in some acetone. Play with the mixture until it comes out to your desired consistency. Make it in a squirt bottle, use it just like epoxy or whatever. This way, the entire work piece is made of ABS plastic so you shouldn't have problems with thermal expansion leading to cracks or separation like you can have with other materials.

If there isn't a tight fit though, Acetone alone might not be enough, and you can either melt a little plastic in Acetone solution to generate filler, or try other plastic-friendly glues that can both fit gaps and bond:

Right, assuming the parts that need to be glued are already a nice snug fit. Plastic welder and/or ABS sludge come in handy when you need to fill a gap though, as is so often the case in carPC-related fabrication.

I'll be experimenting with a few of these soon and will update with my results. Science!

My Son and I were at the Legoland Discovery Center in Grapevine, TX yesterday. We spoke with a LEGO® Certified Master Builder. We asked him and he says that LEGO® uses MEK to permanently adhere their large Lego sets together (lifesize etc). We just finished putting together the Volkswagen T1 Camper Van. It is notorious for the roof coming apart, as is the usual lego problem of the walls around doors often come apart. Well, the MEK we got from Lowes today TOTALLY fixed it. In less than 3 minutes a part was VERY secure and won't come apart. You have to work fast as it is immediately affecting the plastic. Honestly, at less than a minute it won't come apart, and if you don't seat them securely, they will fuse out of place, so be careful. It didn't take more than a VERY light glaze with a paintbrush. I am SOLD and wish we had this years ago!

While MEK is indeed what LEGOland parks use, keep in mind that it does indeed fuse bricks together (don't even think about disassembling the model, ever); and more importantly that its fumes are dangerous.
–
Joubarc♦Mar 15 '13 at 8:04

Cyanoacrylate-based hobby glues with thick viscosity seemed the most effective. The only problem was, when immersed in water the clear LEGO windows fogged up. (No solution to that so far.) Zap a Gap hobby glue offered best results.

ABS plumbing glue worked but was difficult to apply. And if too much was applied, plastic disfigured from the inside out.

Cheap hobby glues all failed for strength, and many disfigured the pieces and were often not thick enough to offer piece manipulation before gluing your hands to it or running down your arm.

Hot melt glue was messy beyond all hell. But worked better than silicone for sealing roofs.

Selley's advanced quick grip (water based) worked, was strong but failed under water. Was also far too time consuming and messy.

Also tried Parfix contact glue. Disfigured the pieces.

Epoxy resin in self-mixing and hand-mixing varieties offered good strength, but was too costly for the job.

That's all I have tested so far, going back to Bunnings and Auto pro.

Last one I tried was a plastic welding glue for sheet plastic and acrylics. Melted pieces from the inside out. But once set, it was indestructible.

MEK is the way to go - it's what the Masterbuilders at the LEGOLAND parks use.
I once brought a miniland sized model from London to the US in my main suitcase that had been glued with MEK and the model was fully intact when I got to the other end!

As others have said, it is VERY nasty when breathed in. Do not even think about using it in confined spaces without a proper extraction system (seriously) and if you get any on your skin wash it off immediately. If you ever spill a bottle of it inside, evacuate the building immediately - believe me, even the LEGOLAND masterbuilders do this if they ever spill it.

Cheapest way to get MEK I have found is go to home depot or somewhere similar and buy some PVC pipe glue - that is MEK (and will say it on the 'ingredients' label).

When gluing - you only need a little brushed onto the brick - easiest to use a syringe of some similar device to put the glue between the studs - then apply the second brick. Wait a few minutes, and it's pretty well welded together.
If gluing a large amount of bricks, do one row at a time and wait a few minutes between rows. Don't rush it or apply too much glue as the bricks will melt.

I use a small bottle of Gorilla super glue for my lego parts. It only squirts a tiny amount to be sure super glue doesn't get all over your parts, and also dries at a mid-range pace. I use it a lot to glue my Tiny Tactical parts to the guns after they come in the mail (which are insanely small parts) and the glue work like a charm.

We tried all kinds. Solvents just didn't cut it and only made the bricks stick tighter. The best we found is actually found at the hardware store in the plumbing aisle.

Oatey all purpose cement is the best we found so far. It contains all the above solvents including MEK (which by the way is either a carcinogen or causes brain damage when absorbed into the body excessively I can't recall) which works well. It is designed specifically for gluing ABS.

We apply it with a small craft paint brush and so far the bond is permanent and allows for plenty of working time without fear of gluing YOURSELF to the bricks.

And it cleans up easily with 100% acetone (hardware store stuf...not nail polish remover as its not concentrated enough).

I use Kragle for putting together the Lego kits, but not any of the removeable pieces or the lego figures. I use a medium viscosity kind of Cyanoacrylate hobby glue. Just have to be careful to not get it on your fingers and your eyes.

So I've been referring to this post for a long time and I figured it is time to put in my experiences. One thing that many answers don't talk about is that different glues are good for different purposes so my input will revolve around that.

A little background. I've been building Lego for multiple decades though only recently started using glue as I've started making art and design for other people through my side business and almost unanimously they want something permanent. I make small delicate designs (I am being intentionally vague here since I don't want to look like I am advertising), mosaics, and large company logos.

The mosaics are made by taking the large grey baseplate and putting a single layer of plates on it (studs out). For this application I use 100% pure acetone. I take a small brush, dip it in the acetone and brush it on a small section of the baseplate and put the mosaic plates on before it dries. Stays together great and if you don't use too much it won't bleed out and mar the look of the mosaic.

For the logos and the small designs, which are built studs up (showing a smooth surface - like building a brick wall), acetone is terrible. Since it melts ABS plastic and is not viscous, it runs along the edges of the bricks creating smudges that don't come out. The end result looks bad especially in those areas where there is a connection between 2 contrasting color bricks. I also tried hobby glue (Testor's Cement Glue) and the results were not great but for different reasons. This glue is very viscous but what happens is when you apply it, it trails thin strands of glue that you need to clean up before it dries. When you squeeze the bricks together (a very tight fit), the glue squirts out and if you wipe it away it mars the glossy surface of the brick. That and that stuff smells so bad it makes you sick. What I have settled on is what Jay mentioned above: Zap-A-Gap. It is viscous enough to not run, does not thin out to strands, doesn't smell nearly as bad as the other glues, and dries really, really strong. I put on a small amount on the back of the brick so that the front surface looks untouched. I just finished a 30" square logo with a Lego frame and I can pick up the piece from its frame without any give. Still looking for a better solution, but Zap-A-Gap is the best for this.

We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.